1. Field of the Invention
The present invention relates to an ink jet recording apparatus and a recording method, in which liquid such as ink is ejected from a fine nozzle, thereby forming a liquid pattern on recording paper or sheet so as to draw characters or graphics.
2. Description of the Related Art
In recent years, a printer using an ink jet recording apparatus has become widely pervasive as a printing apparatus for a personal computer or the like because of easy handling, excellent printing performance, a low cost or the like. Such ink jet recording apparatuses include various types, for example, a thermal type in which bubbles are generated in ink by thermal energy so as to eject ink droplets by pressure waves caused by the bubbles, an electrostatic type in which ink droplets are sucked to be ejected by electrostatic force, a piezoelectric type in which vibrator such as a piezoelectric element is used, or the like.
Furthermore, there has been proposed an amalgam of a piezoelectric system and an electrostatic system. For example, an amalgam of a piezoelectric system and an electrostatic system is disclosed in Japanese Patent Application Laid-Open No. 5-278212, which will be explained below in reference to FIG. 15. In FIG. 15, reference numeral 110 denotes a nozzle from which ink is ejected; 112, a pressure chamber communicating with the nozzle 110 and containing the ink therein; 115, a piezoelectric element for applying a pressure to the pressure chamber 112; 120, a convex ink meniscus formed at the tip of the nozzle 110; 108, a charging electrode for electrically charging the ink portion forming the ink meniscus 120; and 104, an opposite electrode disposed opposite to the charging electrode 108 via a recording sheet 107. A high voltage is applied between the charging electrode 108 and the opposite electrode 104 by a high voltage power source 105.
With this configuration, first, a voltage is applied to the piezoelectric element 115, so that a volume of the pressure chamber 112 is reduced by force generated by the piezoelectric element 115, thereby forming the ink meniscus 120 at the nozzle 110. Subsequently, when the ink meniscus 120 is electrically charged by the charging electrode 108, the ink is ejected from the ink meniscus 120 toward the opposite electrode 104 by an electric field formed between the charging electrode 108 and the opposite electrode 104. At this time, since the recording sheet 107 is interposed between the ink meniscus 120 and the opposite electrode 104, an ink image is formed on the recording sheet 107.
In FIG. 15, although the ink meniscus 120 is formed by the piezoelectric element 115, an ink droplet may be ejected. Normally, as the voltage to be applied to the piezoelectric element 115 is made higher, the diameter of the ink droplet to be ejected becomes greater and the ejection rate of the ink droplet becomes higher. In contrast, as the voltage to be applied to the piezoelectric element 115 is made lower, the diameter of the ink droplet to be ejected becomes smaller and the ejection rate of the ink droplet becomes lower. In the configuration shown in FIG. 15, it is possible to accelerate the ink droplet by electrostatic force and enhance the flying stability of the ink droplet even in the case where the voltage applied to the piezoelectric element 115 is made lower so that the diameter and ejection rate of the ink droplet to be ejected is made smaller and lower, respectively. Moreover, as the diameter of the nozzle 110 becomes smaller, clogging or the like is more liable to be generated and a manufacturing yield becomes worse. Consequently, in the ink jet recording apparatus, it is very useful to eject an ink droplet having a small diameter from a large-diameter nozzle. Therefore, in the configuration shown in FIG. 15, it is possible to provide an ink jet head in which the flying stability of a small-diameter droplet ejected from a large-diameter nozzle can be enhanced, clogging of the nozzle can be reduced, and a good manufacturing yield can be achieved.
However, although in the method illustrated in FIG. 15 a small droplet ejected from a nozzle having a large diameter is accelerated in an electrostatic field so as to enhance the flying stability of the ink droplet, the flying rate of the ink droplet is low since the ejection rate of the ink droplet is low. At the low flying rate of the ink droplet, a deviation of an impact position on the recording sheet 107 becomes great due to variations in flying rate, thereby deteriorating a quality of an image There arises no problem in the case where the relative moving speed between the recording sheet 107 and the nozzle 110 is low; whereas in the case where it is high, the deviation of the impact position becomes too great to be practical.
Additionally, in the case where the voltage to be applied to the piezoelectric element 115 can be varied so that the volume of the droplet to be ejected is changed for dot modulation in the method illustrated in FIG. 15, there arises the deviation of impact positions of a large dot (a large droplet) and a small dot (a small droplet) on the recording sheet 107. Although the deviation of the impact positions can be reduced more in the case where the electrostatic field is applied than in the case it is not applied, the deviation of the impact positions becomes too great to be practical in the case where the relative moving speed between the recording sheet 107 and the nozzle 110 is high.
The present invention has been accomplished in an attempt to solve the above problems observed in the prior art. An object of the present invention is to provide an ink jet head recording apparatus in which clogging in a nozzle can be reduced and a manufacturing yield is favorable by reducing the deviation of an impact position of an ink droplet in the case where a small droplet is ejected from a large-diameter nozzle.
Furthermore, another object of the present invention is to provide an ink jet recording apparatus in which dot modulation can be achieved by reducing the deviation of impact positions of a large droplet and a small droplet on a recording sheet.
One aspect of the present invention is an ink jet recording apparatus comprising:
an ink jet head for ejecting ink from a nozzle;
relative movement means for relatively moving said ink jet head and a recording sheet;
an opposite electrode disposed at a position opposite to said ink jet head; and
voltage applying means for applying a voltage between said ink and said opposite electrode;
wherein an ejection direction of the ink to be ejected from said nozzle is inclined with respect to a direction of an electric field generated by said voltage applying means and has a component in a relative movement direction of said ink jet head relative to said recording sheet.
Another aspect of the present invention is an ink jet recording apparatus, wherein the direction of said electric field signifies a direction of an electric field in the vicinity of said opposite electrode;
the ejection direction of said ink being inclined with respect to the direction of said electric field signifies the ejection direction of said ink being inclined with respect to a plane perpendicular to the relative movement direction by said relative movement means; and
the ejection direction of the ink to be ejected from said nozzle is parallel to or within a plane including a perpendicular line drawn from said nozzle down to said opposite electrode and a straight line drawn from said nozzle toward the relative movement direction by said relative movement means.
Still another aspect of the present invention is an ink jet recording apparatus, wherein said ink jet head includes: a pressure chamber containing said ink therein; the nozzle communicating with said pressure chamber and ejecting the ink; and pressure applying means for applying a pressure to said pressure chamber.
Yet another aspect of the present invention is an ink jet recording apparatus, further comprising pressure varying means for varying the pressure of said pressure applying means, so as to vary a quantity of the ink to be ejected from said nozzle.
Still yet another aspect of the present invention is an ink jet recording apparatus, wherein said pressure applying means includes a vibrating plate attached to said pressure chamber and a piezoelectric element for vibrating said vibrating plate, and said pressure varying means switches an energizing waveform to said piezoelectric element.
A further aspect of the present invention is an ink jet recording apparatus, wherein a nozzle surface having an ejection port of said nozzle is arranged slantwise with respect to a plane perpendicular to a perpendicular line drawn from said nozzle down to said opposite electrode, and said ink is ejected perpendicularly to said nozzle surface.
A still further aspect of the present invention is an ink jet recording apparatus, wherein a nozzle surface having an ejection surface of said nozzle is arranged in parallel with respect to a plane perpendicular to a perpendicular line drawn from said nozzle down to said opposite electrode, and said ink is ejected slantwise to said nozzle surface.
A yet further aspect of the present invention is an ink jet recording apparatus, wherein the axis of said nozzle is inclined with respect to said nozzle surface.
A still yet further aspect of the present invention is an ink jet recording apparatus, further comprising:
relative moving speed switching means for switching a relative moving speed between said ink jet head and said recording sheet which are relatively moved by said relative movement means; and
ejection angle switching means for switching an ejection angle of the ink according to the relative moving speed between said ink jet head and said recording sheet.
One aspect of the present invention is an ink jet recording apparatus, wherein said relative movement means allows a shuttling operation of said ink jet head with respect to said recording sheet, the ink being ejected from said nozzle during both an advancing operation and a returning operation, wherein the ejection directions of ink droplets during the advancing and returning operations are symmetrical with respect to a plane perpendicular to the relative movement direction by said relative movement means.
Another aspect of the present invention is an ink jet recording method comprising the steps of:
inputting a desired recording quality;
switching a relative moving speed of an ink jet head for ejecting ink from a nozzle onto a recording sheet according to said recording quality; and
switching an ejection direction of the ink to be ejected from said nozzle according to said relative moving speed.
Still another aspect of the present invention is an ink jet recording method, wherein the ejection direction of said ink is inclined with respect to a plane perpendicular to said relative movement direction, and has a component in the relative movement direction of said ink jet head with respect to said recording sheet.
Yet another aspect of the present invention is an ink jet recording method comprising the steps of:
determining a relative movement direction of an ink jet head for ejecting ink from a nozzle onto a recording sheet; and
switching an ejection direction of the ink to be ejected from said nozzle according to said relative movement direction;
wherein the ejection direction of said ink is inclined with respect to a plane perpendicular to said relative movement direction, and has a component in the relative movement direction of said ink jet head with respect to said recording sheet.
Still yet another aspect of the present invention is an ink jet recording method, wherein said ink jet head or said recording sheet performs a shuttling operation, the ejection directions of said ink during advancing and returning operations are symmetrical with respect to the plane perpendicular to said relative movement direction.